Hepatitis C virus (hereinafter referred to as HCV) is a virus which belongs to Flaviviridae and has a genome of a single-stranded (+)-strand sense RNA, and known to cause hepatitis C. Recent studies have revealed that HCV can be divided into many types based on the genotype or the serotype. According to a phylogenetic analysis by Simmonds et al. using nucleotide sequences of HCV strains, HCV can be divided into 6 types, that is, the genotype 1a, genotype 1b, genotype 2a, genotype 2b, genotype 3a and genotype 3b, each of which can be further divided into several subtypes (Non-patent Document 1).
At present, therapy for hepatitis C is carried out mainly with interferon-α or interferon-β, or by a combination therapy using interferon-α and a purine nucleoside-derivative ribavirin. However, even in cases where these therapies are carried out, a therapeutic effect can be observed in only about 60% of the overall patients, and, even in cases where the effect was observed in patients, recurrence occurs in more than half of the patients if the therapy was discontinued. The therapeutic effect of interferon is known to be correlated with the genotype of HCV, and it is said that the effect is low against the genotype 1b while the effect is high against the genotype 2a (Non-patent Document 2).
Therefore, in order to evaluate the effect of an agent, it is important to establish a system which allows infection with, and growth of, each type of the virus, and to thereby investigate the effect of the agent against each type of the virus.
Until recently, growing of HCV in a cell culture system and infection of cultured cells with HCV had been difficult, and the only animal which can be infected with HCV and can be used in experiments was chimpanzee, so that research on the replication mechanism of HCV and on its infection mechanism had been difficult. However, recently, HCV subgenomic RNA replicons were prepared as HCV-derived RNAs having self-replication capacity (Patent Document 1; Non-patent Document 3; Non-patent Document 4; Non-patent Document 5), and analysis of the replication mechanism of HCV using cultured cells became possible. These HCV subgenomic RNA replicons were prepared by replacing structural proteins existing in the downstream of HCV IRES in the 5′-untranslated region of the HCV genomic RNA of the clone called Con1, which belongs to the genotype 1b, with a neomycin resistance gene and EMCV-IRES linked to the downstream thereof. It has been demonstrated that introduction of the RNA replicons into Huh7 human liver cancer cells followed by culturing of the cells in the presence of neomycin allows self-replication of the replicons in the Huh7 cells. It is considered that the systems for evaluation of replication of HCV using this RNA replicon system can be a powerful tool for development of anti-HCV drugs
However, since encoded viral proteins are different among HCVs having different genotypes, sufficient elucidation of the replication mechanism of HCV is difficult by only analyzing a subgenomic RNA replicon derived from HCV of the genotype 1b. Therefore, it is thought that preparation of HCV RNA replicons of many genotypes is necessary for research on the replication mechanism of HCV and anti-HCV drugs.
In Patent Document 2, identification of the virus and the genomic sequence are disclosed for the JFH-1 strain, which belongs to the 2a type. Further, in Patent Document 3, the JFH 2.1 strain and 2.2 strain, which similarly belong to the 2a type, and preparation of replicon RNAs using them are disclosed. On the other hand, in terms of the 1a type, there is a report on the H77 strain (Non-patent Document 6), but a recombinant virus obtained from this strain does not have a sufficient replication efficiency. Further, although a replicon was successfully prepared by introduction of 5 types of mutations which were predicted based on the 1b type, this replicon could be replicated only in a special cell.